The potential profile and quantum energy level in ZnSe/CdSe/ZnSe strained quantum well grown on vicinal GaAs(001) substrate are calculated. The potential in CdSe at the step edge is increased due to the strain inhomogeneity for both electron and heavy hole. As a result, the lateral length of CdSe well decreased compared with the terrace width. The strain-induced potential modulation raises the quantum energy level. The shift of quantum energy level in conduction band increases with substrate vicinal angle whereas no significant shift is found for valence band because of large effective mass of heavy hole. The shift of quantum energy level increases with increasing weil width for thin well, however, it decreases for wide well. Carrier confinement in the terrace region is hardly found since the wave function shows undulation of only 2% in the substrate vicinal direction.